1. Field of the Invention
The present invention relates to a method of compensating for image quality of an inkjet printer, and more particularly, to an apparatus for and a method of compensating for image quality of an inkjet printer which can allow a user to select a level of shingling.
2. Description of the Related Art
An inkjet printer generally performs printing on paper by ejecting ink from thin nozzles of a printhead, and a spray mode (ink-jetting type) of the printhead of the inkjet printer is largely divided into a piezo-type and a thermal-type. In the thermal-type, ink is sprayed through nozzles by instantaneously applying heat to an ink chamber containing ink. In the piezo-type, ink is sprayed by a deformation to a piezo-actuator.
The inkjet printer includes a printhead spraying ink through nozzles irrespective of the ink-jetting type. The printhead has the nozzles to eject ink corresponding to each color of yellow (Y), magenta (M), cyan (C) and black (K) arranged in a sub-scanning direction, that is, in a paper feeding direction.
A printing process of a general inkjet printer is processed such that the printhead having nozzles for the respective colors prints a line on a sheet of paper while reciprocating in a main scanning direction perpendicular to the sub-scanning direction, and then the sheet moves (is fed) in the sub-scanning direction to allow the printhead to be disposed on a next line on the paper. As an example, printing is performed by the printhead with five nozzles arranged in the sub-scanning direction.
The general inkjet printer is provided with a plurality of nozzles, and a recent trend is toward providing a greater number of nozzles in order to improve the image quality. The image quality of the inkjet printer largely depends on a performance of the nozzles, and a deviation of a dot size or a dot position varying according to a difference in the performance of the nozzles results in a change in the image quality. In the general inkjet printer, as the printing is repeated, the nozzles deteriorate more severely, resulting in a considerable difference in the performance of the nozzles. Unlike a case as shown in FIG. 1 showing an ideal printing result, if there is any malfunctioning (defective) nozzle, the image quality of the inkjet printer is lowered as shown in FIG. 2A. Referring to FIG. 2A, a raster, that is, a row of dots ejected from a defective nozzle and printed in a group in the main scanning direction, is shown on a printed matter (sheet). If such rasters occur repeatedly, the image quality of the printed matter sharply deteriorates. The group of dots printed by a nozzle in the main scanning direction is referred to as the raster, and a line (image) may include a plurality of rasters (raster lines).
In order to prevent the image quality from deteriorating due to the defective nozzle, the printhead should be entirely replaced with a new one, which is, however, uneconomical. In particular, in a case where a printhead and an ink cartridge are incorporated with each other, it may often happen that a user has to either continue printing materials, which have lowered the image quality, or replace the ink cartridge before ink is fully consumed.
To compensate for the image quality lowered due to the defective nozzle, one approach to the lowered image quality is to program a printer driver of the inkjet printer to perform shingling. The term “shingling” refers to a method of controlling a printer in a software manner to provide temporal and spatial intervals necessary for drying a printed line prior to printing another image (line). That is to say, in a shingling mode, the printer prints a raster of the image only a predetermined percentage of total ink dots available in a given print pass with the defective nozzle and makes another pass to complete the raster with a normal nozzle, thereby preventing ink from draining, spreading, or forming a stain and to minimize a deviation in the performance between the nozzles.
FIG. 2B shows a result of printing by 50% shingling. With the 50% shingling as shown in FIG. 2B, a normal nozzle prints normal ink dots on a defective raster while alternately moving an odd-number raster row and an even-number raster row, which have not been printed properly, leading to good print quality.
As a shingling level increases, the percentage of the shingling is reduced. For example, 50% shingling is a higher level than 33% shingling, and 25% shingling is a higher level than 33% shingling.
FIG. 3 shows a printer driver system of the general inkjet printer, equipped with a control mode changing predetermined characteristics of image data from input image data to output image data.
Referring to FIG. 3, if the image data is input to a computer 11, a resolution, a color, a tone and a pixel position of the input image data are converted by a rendering module 13, a color converting module 15, a halftone module 17 and a shingle module 19, all contained in a printer driver 10, to the output image data to be output to a printer 21.
In the general inkjet printer, a shingling mode as well as a rendering converting mode, a color converting mode and a halftone module are previously set at a manufacturing time of the inkjet printer. Thus, in a case where an ink cartridge and a printhead are incorporated with each other, if any nozzle of the printhead is defective, there is no method of compensating for the image quality. Moreover, although the ink cartridge can be effectively used, both the defective printhead and the non-defective ink cartridge must be replaced with a new set to maintain the image quality.